The invention relates to an exhaust gas turbocharger for an internal combustion engine including a turbine with a variable guide vane structure supported in the turbine inlet flow passage by a support ring.
Document DE 102 37 413 A1 discloses an exhaust gas turbocharger, which comprises an exhaust gas turbine in the exhaust line of the internal combustion engine and a compressor in the intake tract, with the turbine wheel of the exhaust gas turbine driving the compressor wheel in the compressor via a shaft. The compressor sucks the combustion air from the environment and compresses it to an increased charge pressure, under which the combustion air is supplied to the cylinders of the internal combustion engine. At the exhaust gas, side of the internal combustion engine, the pressurized exhaust gases of the internal combustion engine drive the turbine wheel.
In order to improve its power output, the exhaust gas turbine is provided with a variable turbine inlet geometry which permits adjustment of the effective inlet flow cross-section to the turbine wheel. The variable turbine geometry (VTG) arrangement can be used to increase power both in the engine operating mode and in the engine braking mode. The variable turbine geometry arrangement is embodied as an adjustable guide vane structure which comprises a support ring with guide vanes disposed at one endface thereof. The guide vanes are situated in the flow inlet cross section and can be pivoted about a rotational axis between a minimum blocking position and a maximum opening position.
The guide vane gap required to ensure efficient operation for rotor blade turbine geometries is determined by the material and the geometry of the guide vanes and by the position and the material of the spacer sleeves which serve to set the cold play of the guide vane structure. A further influential variable is the misalignment, resulting from thermal and mechanical loading, between the two running faces (the end face of the guide vane support ring and the Machined facing contour of the turbine housing) at which the guide vanes should terminate with the smallest possible gap. Since the spacing between the two running faces is generally determined by only three spacer sleeves, it is possible, in particular in the case of large exhaust gas turbines, that the operating gap varies significantly from one guide vane to another. This has the result that, for example in the event of a fast rise in the exhaust gas temperature, the spacer sleeves heat up and expand significantly more slowly than the guide vanes.
In order to prevent the guide vanes from becoming jammed with the smallest gap, it is therefore necessary to provide a relatively large cold play and to accept corresponding losses in efficiency.
It is the object of the present invention to improve the efficiency of exhaust gas turbochargers using simple means. Gaps between the end sides of guide vanes in the flow inlet cross section and the adjacent housing wall should expediently be reduced by design features causing no energy consumption.